Adhesive compositions are used to affix (bond) glass (windows) into buildings and vehicles, see Rizk, U.S. Pat. No. 4,780,520; Bhat, U.S. Pat. No. 5,976,305; Hsieh et al, U.S. Pat. No. 6,015,475 and Zhou, U.S. Pat. No. 6,709,539, all incorporated herein by reference. In automobile factories, windows are installed using robots and computer controlled processing which facilitates the use of a variety of high performance adhesives, for instance, nonconductive adhesives and high modulus adhesives. These adhesives have to be storage stable and be readily applied under high shear, for example, to a windshield, while retaining the bead shape so that the windshield can be properly fitted to the automobile. This typically has been achieved by one part moisture curable polyurethane prepolymer based adhesives having fillers, with the prepolymers having sufficient molecular weight, so that they are still pumpable and can be applied to the windshield without sagging or stringing in the time it takes to place the windshield on the automobile.
The need for sufficient molecular weight of the prepolymer causes the prepolymer to have tight quality control so that it is still pumpable and yet storage stable for long periods of time. Unfortunately, these opposite characteristics make for rather narrow windows for making adhesives that do not suffer from pumping or sagging issues arising in an automated plant, particularly when the adhesive must undergo high shear from pumping, prior to being applied.
Sag is the loss of the shape of the adhesive bead, often as the result of gravitational forces. If severe enough, this deformation can interfere in the proper installation and sealing of the window into the vehicle. Stringing of an adhesive is the formation of a long string of adhesive at the end of the bead of adhesive dispensed which can complicate application of the adhesive and cause imperfections in the installed adhesive bead. Thus, a replacement window installer often has to carry a variety of adhesives so that the installer can match the adhesive to the properties of the original adhesive.
In contrast, when a vehicle needs a window replaced, it is often performed in a remote location by an installer working from a vehicle. In this environment, speed of cure is important as the vehicle owner desires to drive the vehicle as soon as possible after installation on the window. Adhesives useful in replacing windows for vehicles which facilitate fast drive away times are known; see Bhat, U.S. Pat. No. 5,976,305 and Zhou, U.S. Pat. No. 6,709,539. The introduction of various high performance adhesive compositions used for installing windows in automobile factories presents a problem for replacement window installers. First, adhesives that meet all the varied performance requirements are not available in the market place. Second, it is difficult to formulate many high performance adhesive compositions to allow rapid drive away times that do not sag or string.
Adhesives have been developed which provide good initial green strength that allows the adhesive to hold the glass in place without additional fixturing to hold the glass in place. This is achieved through the inclusion of crystalline polyesters in the adhesive. These adhesives have hot melt properties that require that the adhesive be melted and applied hot; see Proebster, U.S. Pat. No. 5,747,581, incorporated herein by reference. The problem with these adhesives is that they require heat and the use of complex equipment for their use. The initial green strength provided is not sufficient for rapid drive away time. Because of the proliferation of hot melt adhesives in the automobile window replacement market, many installers insist on heating adhesives prior to applying the adhesive to the window or the window flange. Many adhesives when heated demonstrate sagging and/or stringing.
What is needed is a composition which is useful as an adhesive for bonding glass into a structure which may be formulated to exhibit a variety of high performance properties (such as high modulus and nonconductive nature), exhibits fast safe drive away times when applied under a variety of conditions, fast strength development, can be applied without the need for heating the adhesive, but may be heated without detrimental consequences, can be applied under a wide range of environmental conditions, does not require expensive ingredients and does not sag or string when applied even after undergoing high shear just prior to being applied.